The present invention relates to a water-base ballpoint pen which has an ink reservoir directly filled with ink. More particularly, the present invention relates to an ink follower to be used at the tail end of the ink in such a water-base ballpoint pen.
The ink for a water-base ballpoint pen has a viscosity of as low as 50 mPaxc2x7sec to 3 Pa.sec, while the ink for an oil-base ballpoint pen of a similar structure to a water-base pen has a viscosity of 3 to 20 Pa.sec. Consequently, the ink filled in a water-base ballpoint pen may leak out when the pen is left upward or sideways.
Moreover, even a small impact made on the pen may cause its ink to scatter and to stain the hand or the clothes. Therefore, the water-base ballpoint pen is equipped with an ink follower for preventing such accidents.
Various types of ink followers for water-base ballpoint pens which have an ink reservoir directly filled with ink, which are consisted of gel-like material or the mixture of gel-like material and solid material, are disclosed in many prior applications such as JP48-40510A, JP57-153070A, JP57-200472A, JP58-1772A, JP61-57673A, JP61-145269A, JP61-151289A, JP61-200187A, JP61-268786A, JP62-50379A, JP62-148581A, JP62-199492A, JP63-6077A, JP02-248487A, JP04-202281A, JP05-270192A, JP05-270193A, JP06-200235A, JP06-220418A, JP06-247094A, JP06-264048A, JP06-328890A, JP06-336584A, JP07-61187A, JP07-173426A, JP07-214974A, JP07-214975A, JP07-242093A, JP07-266780A, JP08-2171A, JP08-11481A, JP08-58282A, JP08-72465A, JP08-90982A, JP08-108679A, JP08-142570A, JP08-183286A, JP08-300873A, JP08-300874A, JP09-11683A, JP09-76687A and so on.
The purposes of these prior arts are to make the ink follower follow the ink smoothly, to make the pen endure the impact when dropped, to prevent the ink from back flow, to give the pen a good appearance, and so on.
Of the above prior arts, the ink followers disclosed in JP08-300874A and JP09-76687A are characterized in that hydrophilic silica serving as a thickener is added to silicone oil as a base oil. The ink follower disclosed in JP09-76687A additionally contains poly (oxyethylene-oxypropylene) polyol. In the other prior arts, disclosed are many types of ink followers in which silicone oil is used as a base oil or which contain hydrophobic silica as a thickener.
However, when hydrophobic silica is used to thicken the silicone oil, there has been some problems that it is difficult to gain a desired viscosity, especially that in the low shear rate range, and that it is difficult to handle such an ink follower for a long-term increase of its viscosity.
As mentioned above, when the ink follower shows the long-term increase of its viscosity, it interferes with smooth ink flow. Consequently, the shortage of the ink flow causes a phenomenon called xe2x80x9cscratchy writing,xe2x80x9d which means that the drawn line with the pen is scratchy and the pen cannot write well.
On the other hand, a use of a small amount of hydrophilic silica ensures the desired viscosity, but has a defect of a long-term decrease of the viscosity.
As mentioned above, the long-term decrease of the viscosity of the ink follower causes the ink follower to flow out through the tail end of the ballpoint pen when the ballpoint pen is left sideways or upward. Thus the ink follower loses its function of preventing ink leakage and evaporation.
The difference in the technical idea between the prior art and the present invention is explained in view of the role of HO(C2H4O)m.(C3H6O)nH (in which each of m and n shows 0 or a positive integer, provided that m+n is not equal to 0) including poly (oxyethylene-oxypropylene) polyol used in the present invention and that of poly (oxyethylene-oxypropylene) polyol used in JP09-76687A. In regard to the comparison described below, explanation is made with poly (oxyethylene-oxypropylene) polyol as an example.
In JP09-76687A, the use of hydrophilic silica is essential. This is because poly (oxyethylene-oxypropylene) polyol is intended to adsorb the hydrophilic groups such as a hydroxyl group on the surface of the hydrophilic silica and to disperse stably in silicone oil.
On the other hand, the particulate silica as an essential factor in the present invention has methyl groups on its surface in place of the hydrophilic groups. Namely, as seen microscopically, methyl groups are bonded on the surface of the Sixe2x80x94O chain as well as dimethylsilicone oil.
Therefore, the hydrophobic particulate silica is likely to exist separately in silicone oil. Since the particulate silica is well dispersed, a network structure, which is a thickening principle of a silica thickener, is unlikely to develop. As a result, the structural viscosity is small, and the viscosity in a low shear rate range is unlikely to be obtained.
When poly (oxyethylene-oxypropylene) polyol is considered as a dispersant as in JP09-76687A, it is believed that poly (oxyethylene-oxypropylene) polyol selectively adsorbs to, and covers over the hydrophilic silica.
However, it is not believed that poly (oxyethylene-oxypropylene) polyol covers over the surface of the hydrophobic silica since the surface of hydrophobic silica is almost occupied with methyl groups, which serve as steric hindrances.
Probably, it is presumed that poly (oxyethylene-oxypropylene) polyol adsorbs to the hydrophilic residues of the hydrophobic silica and that the viscosity increases by its function of bonding between the silica particles. This will be rather opposite to the idea of the present invention that xe2x80x9cthe dispersant disperses the particles more finely and more stably.xe2x80x9d
In the present invention, poly (oxyethylene-oxypropylene) polyol serves as a weak crosslinking agent between hydrophobic silica particles. Similar discussion can also be made for as methylphenylsilicone oil, alkyl-modified silicone oil etc., which have no hydrophilic groups.
This means the critical difference in the technical idea between the invention in JP09-76687A and the present invention.
Namely, the use of poly (oxyethylene-oxypropylene) polyol in JP09-76687A has a purpose of xe2x80x9cstabilization of dispersionxe2x80x9d. On the other hand, poly (oxyethylene-oxypropylene) polyol in the present invention is used to obtain a viscosity of the ink follower by the interference of the hydrophilic residue of hydrophobic silica with the stable suspension system that comprises hydrophobic silica and silicone oil.
The invention disclosed in JP09-76687A is an excellent technique of dispersing hydrophilic silica, though essentially immicible, stably in silicone oil. However, since there occurs long-term reactions between the adsorbed polyol chains and hydrophilic groups covering over the surface of the silica, the stabilization of dispersion proceeds further and the viscosity is lost. Moreover, it has disadvantages such as a striking acid smell due to an oxidation of decomposed polyol chains.
In the present invention, on the other hand, chemical reaction is unlikely to occur. Moreover, since the long-term unstable factor of hydrophilic residues, which are slightly remained on the surface of hydrophobic silica, is intentionally utilized, the particulate silica is prevented from forming a network structure to give a long-term strong structural viscosity, thus providing an effect of preventing the long-term increase of the viscosity of the ink follower.
The present invention is to provide an ink follower composition for water-base ballpoint pens, which is prevented from long-term change of viscosity and always keeps its initial performance irrespective of the ingredients of the ink.
Moreover, the invention is to provide an ink follower having the ability to shield ink from outer air to prevent the ink from evaporating (anti-evaporation), the ability to prevent ink from leaking out through the tail end of the ink reservoir after writing with the pen upward (anti-leakage), the ability to minimize its adhering amount onto the inner wall of the ink reservoir and to retain its function to follow ink to the last (following ability).
We, the present inventors, have endeavored to study the objects mentioned as above, and, as a result, have found that, when using hydrophobic silica in silicone oil, HO(C2H4O)m.(C3H6O)nH (in which each of m and n shows 0 or a positive integer, provided that m+n is not equal to 0) has a specifically thickening effect and gives the ink follower long-term stable pseudoplasticity. On the basis of these findings, we have completed the present invention.
Namely, the present invention utilizes the specific thickening effect in a system of silicone oil and hydrophobic silica. Accordingly, the non-volatile or hardly-volatile solvent to be the base oil for use in the present invention must consist essentially of silicone oil.
Further, mineral oils, animal or vegetable oils, esters, high-boiling-point hydrocarbons, higher fatty acids, higher alcohols, low-molecular polyolefins and the like may be added for the present invention. However, since the essential base oil is silicone oil, the additional amount of above-mentioned oils is dependent on their compatibility and miscibility with silicone oil. Concretely, the list of silicone oil for use in the present invention includes dimethylsilicone oil, methylphenylsilicone oil, and alkyl-modified silicone oil. Each of them may be used individually, otherwise some of them may be mixed for use.
Amino-modified silicone oil, polyether-modified silicone oil, fatty acid-modified silicone oil and the like are unfavorable for the essential base oil since poly (oxyethylene-oxypropylene) polyol has little effect for assistance of thickening in these oils and since the dispersion stability of hydrophobic silica in these oils is relatively lower than that in dimethylsilicone oil, methylphenylsilicone oil or alkyl-modified silicone oil. However, these oils are sometimes added supplementarily.
Surface-methylated particulate silica is used as the thickener in the present invention. However, hydrophobic inorganic particulate thickener is presumed to have a similar effect.
Moreover, Specific examples of HO(C2H4O)m.(C3H6O)nH (in which each of m and n shows 0 or a positive integer, provided that m+n is not equal to 0) are ethylene glycol, polyethylene glycol, poly (oxyethylene-oxypropylene) polyol, polypropylene glycol, propylene glycol, etc. Needless to say, any other compounds can be used as long as they satisfies the formula. In the compounds that satisfies the formula, (C2H4O) and (C3H6O) may have any desired configuration including, for example, alternate blocks and random blocks.
The ink follower composition in the present invention usually contains a singular base oil or the mixture of this oil and supplementary non-volatile or hardly-volatile solvent. To the base oil, hydrophobic silica is added and kneaded homogeneously in a disperser such as a triple roll mill, a kneader, a ball mill, a bead mill, a basket mill or the like.
It is preferable that HO(C2H4O)m.(C3H6O)nH (in which each of m and n shows 0 or a positive integer, provided that m+n is not equal to 0) is either mixed homogeneously when the base oil is mixed, or added after the hydrophobic silica disperses homogeneously.
This is because there sometimes occurs uneven viscosity when the HO(C2H4O)m.(C3H6O)nH (in which each of m and n shows 0 or a positive integer, provided that m+n is not equal to 0) is first adsorbed to the powdery hydrophobic silica.
So far as the ingredients being mixed could receive sufficient shearing force to form the intended homogeneous mixture, for example, in the case of using a disperser, such as a triple roll mill, with a strong shearing force, the order of adding the ingredients is not specifically defined.
As mentioned above, the ink follower for water-base ballpoint pens in the present invention can well retain its initial properties even when its initial viscosity is suitably prepared and have excellent long-term stability.